Developing apparatus

ABSTRACT

The apparatus uses a corona discharge electrode at the developing station which governs the application of developing powder to nonimage areas of the member. The electrode is provided with a control device that automatically regulates the corona emission of the former as a function of the conductivity of the paper base of the member. The control device includes conductors which electrically couple the base with a source of electrical power and the electrode to sense the conductivity of the base.

United States Patent Robert G. Blanchette Elk Grove Village, Ill.

Nov. 14, 1968 Jan. 12, 1 97 l Addressograph-Multigraph Corporation MountProspect, Ill.

a corporation of Delaware [72] Inventor [21 Appl. No. 22] Filed [45]Patented [73] Assignee [54} DEVELOPING APPARATUS 12 Claims, 2 DrawingFigs.

[52] US. Cl. 118/8, 1 18/637; 250/495: 317/262; 324/65 [51] Int. Cl. tB05c 11/00 [50] Field ofSearch 118/4, 8,

637, LX, 638, 624; l l7/17.5, 37LX, Control Digest; 324/65(Inquired);250/49.5, (6.1, 6.2); 317/4, 262A, 262

[56] References Cited UNITED STATES PATENTS 2,273,941 2/1942 Dorn 1l7/(Control-Dig.)

2,918,900 12/1959 Carlson 118/637 2,956,487 10/1960 Giamo, Jr. (118/637)3,182,573 5/1965 Clark et al. 1l8/637(C)X 3,244,083 4/1966 Gundlach 118/637X 3,257,222 6/1966 Carlson 118/637X 3,404,418 Fantuzzo ll8/637XPrimary Examiner-Morris Kaplan AttorneySol L. Goldstein ABSTRACT: Theapparatus uses a corona discharge electrode at the developing stationwhich governs the application of developing powder to nonima'ge areas ofthe member. The electrode is provided with a control device thatautomatically regulates the corona emission of the former as a functionof the conductivity of the paper base of the member. The control deviceincludes conductors which electrically couple the base with a source ofelectrical power and the electrode to sense the conductivity of thebase.

DEVELOPING APPARATUS BACKGROUND OF THE INVENTION This invention relatesto an improved developing apparatus useful in developing a latentelectrostatic'image retained on the light-sensitive photoconductivesurface of a photoelectrostatic recording member. More particularly,this invention relates to'an apparatus of the above type which iscapable of monitoring the base portion of the recording member, sensinga change in conductivity due to a corresponding change in the moisturecontent thereof brought about by a change in humidity of the surroundingatmosphere, and in accordance therewith ultimately controlling theapplication of electroscopic developing powder to the nonimage surfaceareas of the member.

A photoelectrostatic recording member imaged in accordance with awell-known photoelectrostatic copying process is developed byselectively applying electroscopic developing powder to the latentelectrostatic image on the photoconductive surface of the member toconvert the image into a visible form. Means for governing theapplication of powder to the nonimage areas on the recording surface,such as disclosed in U.S. Pat. No. 3,369,917, assigned to the sameassignee, are frequently employed in the photoelectrostatic copying art.Devices of this type generally include a source of electrical power and,an electrode coupled to the source, disposed adjacent themoisture-sensitive base. A current provided by the electrode impingesupon the recording member. A voltage opposite in polarity from that ofthe face or photoconductive surface of the recording member is therebyproduced and in turn causes the repulsion of the powder from thenonimage areas of the latter. Thus, background areas thereon aremaintained free of unwanted, spurious powder deposition. In the case ofa corona-type electrode which is commonly used for biasing purposes, thecurrent or voltage produced thereby is dependent upon the potentialdifference between a discharge wire and a shield portion making up theelectrode. A change in the conductivity of the base of the recordingmember disrupts the repelling of unwanted powder deposition on thebackground areas of the photoconductive layer of the recording member sothat the. utilization of the corona bias voltage becomes less efficientwhen the conductivity of the base is great.

In the case wherein the base employed is paper, the humidity of thesurrounding atmosphere effects its conductivity. As the moisture contentof the base increases, the base becomes more conductive. When the baseis'in a highly conductive state, the amount of current being supplied bythe electrode which generates the bias voltage to the recording memberfor the purpose of repelling electroscopic developing powder from thenonimage areas thereof, must be increased, since the base tends, at thistime, to conduct current laterally therealong, establishing a shuntcircuit on the backside of the recording member.

Prior art devices are provided with manually operated controls forvarying the current being supplied by the electrode to maintain the biasvoltage on the recording member. Necessarily, such known devices mustrely on the judgement of the operator to properly assess the moisturecondition of the base. Frequently, as a result of errors in judgement onthe part of the operator, improper development of the recording memberoccurs.

SUMMARY OF THE INVENTION Accordingly, it is a primary object of thepresent invention to provide an improved developing apparatus whichprevents automatically the deposition of electroscopic developing powderon the nonimage areas of the photoconductive surface of a recordingmember as a function of the conductivity of the base of the member.

In accordance with the foregoing object, the developing apparatus ofthis invention includes a developer assembly for applying electroscopicpowder to the photoconductive surface of the recording member, therebyreducing the latent electrostatic image on the surface to a visibleform; means for govern the application of the powder to the nonimageareas on the surface including a source of electrical power and coupledto the source, an electrode disposed adjacent the moisture-sensitivebase, the electrode imparting a bias voltage to the member opposite tothat on the face or photoconductive surface thereof to repel the chargedpowder from the nonimage areas; and means connected to the governingmeans for monitoring the conductive state of the base portion of therecording member and in accordance therewith, controlling automaticallythe energization of the electrode. The monitoring or sensing means inone embodiment of the invention comprises a pair of insulatively spacedconductors, each in electrical contact with the base. The conductors areelectrically coupled to the electrode and power source, so that as theconductivity of the base changes, the current supplied by the electrodeis varied accordingly to maintain the bias voltage at a proper level.The base, in effect, acts as a variable resistor changing itsresistivity as a function of the conductivity thereof.

In the preferred embodiments of this invention, a conven tional magneticbrush applicator is employed, and the electrode used is of the coronatype which includes at least one discharge wire surrounded inpart by aconductive shield. The corona electrode establishes a corona current toground through an air dielectric and the member. The base can be coupledeither between the power source and discharge wire or between the shieldand ground.

DRAWINGS For a better understanding of this invention, as well as otherobjects and features thereof, reference is had to the accompanyingdrawings in which:

FIG. 1 is a perspective view of one embodiment of the present inventionwherein the base is connected between the shield of the corona electrodeand ground, and

FIG. 2 is a schematic drawing of another embodiment of this inventionwherein the base is connected between a source of electrical power andthe discharge wire of the corona electrode.

DETAILED DESCRIPTION Referring to FIG. 1, there is shown one embodimentof the developing apparatus of this invention, indicated generally as10. The apparatus 10 includes a conventional magnetic brush developingassembly 12, 7 comprising a rotatably mounted cylinder 14 and a magneticbrush 16, made up of magnetic carrier particles and electroscopicdeveloping powder, herein, having a positive polarity. A coronaelectrode 18 is connected to the positive terminal of a DC power source22, and means, indicated generally as 28, are provided for controllingthe operation of the electrode 18 in accordance with the conductivity ofthe base 24 of the photoelectrostatic recording member 26 beingdeveloped, thereby to regulate the bias voltage, which is of the samepolarity as the developing powder for repelling unwanted powderdeposition on the nonimage areas of the photoconductive surface of therecording member.

The member 26 is conveyed past assembly 12 by a pair of driven rollers30 and 32, the exterior coverings of which are formed of an insulatingmaterial, such as rubber or nylon. As the member 26 is moved past theassembly 12, the photoconductive layer 34, bearing a latentelectrostatic image thereon of a negative polarity in this case, comesinto tangential contact with the magnetic brush 16 whereby powder isapplied to the latent image to convert it into a visible form. Thecylinder 14 is as long axially as the member 26 is wide, is disposedtransversely to the path of movement of the member, and is connected toground. Many suitable magnetic developing assemblies are available, suchas, for example, of the type disclosed in detail in U.S. Pat. No.3,003,462.

The upper roller 30, as shown in FIG. 1, is formed into separate halves38 and 40. Each half is supported on a corresponding metallic,electrically conductive half shaft 38a and 40a, respectively. A pair ofmetallic, conductive discs 44 and 46 are fixedly mounted on respectiveopposing end portions 38b and 40b of the half shafts 38a and 40a so asto be both mechanically and electrically connected thereto, and acylindrical insulating spacer element 42 of a plastic, rubber or thelike material (shown in Section in FIG. 1) is interposed between theopposing end portions 38b and 40b with the latter being imbedded inrespective ends thereof without making contact with each other. Thediameter of each of the discs 44 and 46 is equal to that of the outerdiameter of the roller 30; thus both the exterior insulating jackets ofthe roller and the conductive outer circumferential surfaces of thediscs are in contact with the base portion 24 of the recording member asit passes between rollers 30 and 32.

The corona electrode 18 disposed above the moisture-sensitive base 24includes a discharge wire 48 connected through a resistor 50 to thepower source 22, and a conductive metal shield 52 which partiallysurrounds the wire. The wire 48, being maintained at a potential in therange of from 4,000- -6,000 volts, ionizes the atmosphere in thevicinity of the wire to establish a corona current flow via the airdielectric between the electrode and recording member 26.

The shield 52 is connected to ground via the circuit including alimiting resistor 53, half shaft 38, disc 44, the base 24, disc 46, andhalf shaft 40.

The corona current flow to ground over the last mentioned path dependson the conductivity of the base 24 which effects the potentialdifference between the wire 48 and shield 52. As mentioned heretofore athigh humidity conditions the base 24 is highly conductive and a shuntcircuit to ground is established which drains off a portion of thecorona current being provided by electrode 18. If this drain in coronacurrent is not compensated for, the bias voltage will be decreasedaccordingly and the background or nonimage areas of the member 26 willreceive a spurious deposition of powder. In order to compensate for thiscurrent drain, the potential difference between the wire 48 and shield52 must be increased.

By coupling the base 24 to the electrode 18, as shown, the potentialdifference between the shield 52 and the wire 48 increases or decreasesin direct proportion with increases or decreases in the conductivity ofthe base, so that, even though a portion of the corona current is beingdiverted at high humidity conditions, a greater amount of current ismade available automatically to maintain the bias voltage on the member26 at a predetermined level.

Explaining this more fully and in more detail, the base 24 of therecording member acts as a variable resistor; that is, the resistance ofthe base portion changes with a variation in moisture content or otherfactors which effect the conductivity of the base. As described above,the greater the moisture content, the greater the conductivity thereof.Thus, by including the base portion 24 of the recording member in thecircuit heretofore described, a change in resistance of the baseproduces a resistance change in the circuit; consequently, the currentflow from the electrode 18 producing the bias voltage, will be affected.

In the embodiment of the invention of FIG. 1, the base 24 is employed asa conductor between discs 44 and 46 to complete the circuit from shield52, through half shaft 38, half shaft 40 and to ground. As theresistivity (conductivity) of the base 24 changes due to a change inmoisture content thereof caused by a variation in the humidity of thesurrounding atmosphere, the current permitted to flow through the lastmentioned circuit is inhibited or enhanced, as the case may be. Thechange in the current flow through the last mentioned circuit in turneffects the current flow from the discharge wire to member 26 and theassembly 12. Thus, when the base becomes highly conductive and a greaterflow of currentis permitted in the circuit comprising shield 52, halfshaft 38, disc 44, base 24, disc 46, and half shaft 40 to ground, thepotential difference between shield 52 and discharge wire 48 is great.In turn a greater current flow is provided from the power source 27,

through wire 48 and the air dielectric. By the same token when themoisture content of the base 24 is small and the base is nearly dry,having relatively no moisture therein, the resistance of the base 24 isvery high and controls the shield circuit. The potential differencebetween the shield 52 and the discharge wire at this time is reduced andconsequently a lesser current flow is provided in the circuit includingthe discharge wire and the air dielectric.

Thus, the arrangement according to the invention automatically adjuststhe potential difference between the discharge wire 48 and shield 52 toin turn control the current flow for repelling unwanted, spuriousdeveloper powder deposition in the background or nonimage areas on thephotoconductive surface of the recording member.

Referring now to FIG. 2 of the drawings, there is shown anotherembodiment of the developing apparatus of the present invention,indicated generally as 60. Developing apparatus 60 comprises a magneticdeveloping assembly 62 which applies developing powder to the latentelectrostatic image 64 on the photoconductive surface 66 of therecording member 68 as it is moved past the apparatus by the rollerpairs 67 and 69, and means for governing the application of powder tothe nonimage area 70 on the'surface 66, made up of a corona electrode 72connected to the positive terminal of a DC power source 74. Thedischarge wire 84 of the electrode 72 is connected to a parallelcombination of resistances made up of resistor 76 and the variableresistance indicated as 78 of the base 79 of recording member. The baseis coupled to the resistor 76 by means of monitoring or sensingconductors 80 and 82 which contact the base 79 at predetermined spacedapart points therealong. The parallel resistance combination is in turnconnected through another resistor to a grounded power source 74.

The operation of this circuit configuration is similar to that of theembodiment of FIG. 1. As the resistance of the base 79 decreases due toa greater moisture content, caused by an increase in the surroundinghumidity, the potential difference between the shield 86 and dischargewire 84 increases causing a greater current flow therebetween, thusmaintaining the bias voltage at a proper level to repel spuriousdeveloper powder deposits on the nonimage areas of the photoconductivelayer 66 of the powder.

In this case the shield 86 of electrode 72 is always at groundpotential, and through the regulation of the potential differencebetween the discharge wire and ground, the bias volt age providedthereby is maintained. plate-type Although the present invention hasbeen described with reference to a number of illustrative embodimentsthereof, it should be understood that other modifications andembodiments can be devised by those skilled in the art that will fallwithin the spirit and scope of this invention. For example, it iscontemplated that the principles disclosed herein can be embodied indeveloping devices using plate-type contact electrodes instead of thepreferred corona electrode.

The aim in the appended claims is to cover all such changes andmodification as come within the true spirit and scope of the invention.

Iclaim:

1. in apparatus for developing a latent electrostatic image retained onthe photoconductive surface of a photoelectrostatic recording member,said member having a moisture-sensitive base supporting said surface,the combination comprismg:

developer means for applying electroscopic powder to the photoconductivesurface of said recording member whereby the latent image is convertedinto a visible form;

a source of electrical power;

electrode means coupled to said power source and disposed adjacent saidbase support, said electrode means providing a bias voltage of apredetermined level to said member for repelling the powder from thenonimage areas; and

means connected to said electrode means for automatically regulating theoperation of said electrode means to maintain said bias voltage at saidpredetermined level in accordance with the moisture content of the baseof said recording member.

2. The combination as defined in claim 1, wherein said automaticregulating means include conductive monitor means in electrical contactwith the base for electrically connecting said base to said electrodemeans and said source.

3. The combination as defined in claim 2, wherein said electrode is ofthe corona-type having at least one discharge wire surrounded partiallyby a conductive shield and which establishes current through an airdielectric to said member.

4. The combination as defined in claim 3, wherein said conductivemonitor means couple said base'between said source and said dischargewire.

5. The combination as defined in claim 3, wherein said conductivemonitor means couple said base in series connection between said shieldand ground.

6. The combination as defined in claim 1, wherein said developer meanscomprises a magnetic brush made up of magnetic carrier particles andsaid powder and wherein the polarity of said powder and said biasvoltage are the same.

7. The combination as defined in claim 1, wherein said electrode meansis coupled electrically through said base support, whereby due to anincrease in the moisture content of said base support, the conductivitythereof increases proportionally, causing a corresponding increase inelectrical current through said electrode means thereby to maintain saidbias voltage at said predetermined level.

8. The combination as defined in claim 7, wherein said regulating meansfurther includes resistance means connected in parallel relation withsaid base support and interposed between said electrode means and saidpower source.

9. In an apparatus for developing a latent electrostatic image retainedon the photoconductive surface of a photoelectrostatic recording member,said member having a base supporting said surface, said base varying inconductivity in accordance with changes in the humidity of thesurrounding atmosphere or the like, the combination comprising:

developer means for applying electroscopic powder of a predeterminedpolarity to the surface of said recording member whereby the latentimage is converted into a visible form;

a source of electrical power;

electrode means coupled to said power source and disposed adjacent saidbase support, said electrode means providing a bias voltage having apolarity the same as that of said electroscopic powder applied to saidmember for repelling the powder from the nonimage areas of thephotoconductive surface of said recording member; and

sensor means coupled to said electrode means and the base support ofsaid recording member for automatically regulating the operation of saidelectrode means to maintain said bias voltage at said predeterminedlevel in accordance with the conductivity of said base support.

10. The combination as claimed in claim 9. wherein said sensor meansincludes a pair of spaced conductors coupled to said base support andconnected to said electrode means, said base support completing acircuit between said conductors, whereby a change in conducting of saidbase support causes a corresponding change in current flow from saidpower source through said electrode means, thereby to maintain the levelof said bias voltage on said member for repelling said electroscopicpowder.

11. in an apparatus for developing a latent electrostatic image retainedon the photoconductive surface of a photoelectrostatic recording member,said member having a moisture-sensitive base supporting said surface,the combination comprising:

developer means for applying electroscopic powder to the surface wherebythe latent image is converted into a visible form;

a source of electrical'power; a corona-type electrode disposed ad acentsaid base support providing an electrical current to said member toproduce a bias voltage of a predetermined level for repelling the powderfrom the nonimage areas of said photoconductive surface and including adischarge wire surrounded partially by a conductive shield, said wirebeing electrically connected to said power source;

a roller member mounted for rolling engagement with said recordingmember along the base support thereof, said roller member includingfirst and second electrically conductive halves insulatively spaced fromeach other, said first roller half being connected to the conductiveshield of said corona electrode and said second roller half beingconnected to ground potential; and

said first and second roller halves being electrically interconnectedthrough said base support, whereby when the moisture content of saidbase support increases, the conductivity thereof increasesproportionally, thereby to in turn maintain said predetermined biasvoltage for the repulsion of developer powder from the nonimage areas ofsaid photoconductive surface.

12. The combination as defined in claim 11, wherein each of said rollerhalves of said roller member comprises a conductive core extendingaxially thereof with a cylindrical insulating jacket formed thereabout,and wherein said roller halves include mounted at opposing ends thereof,electrically conductive disc members, each of which is connected to arespective one of said conductive cores of said roller halves, said discmembers being joined by means of an insulating spacer and being inrolling engagement with the base support of said recording member.

1. In apparatus for developing a latent electrostatic image retained onthe photoconductive surface of a photoelectrostatic recording member,said member having a moisture-sensitive base supporting said surface,the combination comprising: developer means for applying electroscopicpowder to the photoconductive surface of said recording member wherebythe latent image is converted into a visible form; a source ofelectrical power; electrode means coupled to said power source anddisposed adjacent said base support, said electrode means providing abias voltage of a predetermined level to said member for repelling thepowder from the nonimage areas; and means connected to said electrodemeans for automatically regulating the operation of said electrode meansto maintain said bias voltage at said predetermined level in accordancewith the moisture content of the base of said recording member.
 2. Thecombination as defined in claim 1, wherein said automatic regulatingmeans include conductive monitor means in electrical contact with thebase for electrically connecting said base to said electrode means andsaid source.
 3. The combination as defined in claim 2, wherein saidelectrode is of the corona-type having at least one discharge wiresurrounded partially by a conductive shield and which establishescurrent through an air dielectric to said member.
 4. The combination asdefined in claim 3, wherein said conductive monitor means couple saidbase between said source and said discharge wire.
 5. The combination asdefined in claim 3, wherein said conductive monitor means couple saidbase in series connection between said shield and ground.
 6. Thecombination as defined in claim 1, wherein said developer meanscomprises a magnetic brush made up of magnetic carrier particles andsaid powder and wherein the polarity of said powder and said biasvoltage are the same.
 7. The combination as defined in claim 1, whereinsaid electrode means is coupled electrically through said base support,whereby due to an increase in the moisture content of said base support,the conductivity thereof increases proportionally, causing acorresponding increase in electrical current through said electrodemeans thereby to maintain said bias voltage at said predetermined level.8. The combination as defined in claim 7, wherein said regulating meansfurther includes resistance means connected in parallel relation withsaid base support and interposed between said electrode means and saidpower source.
 9. In an apparatus for developing a latent electrostaticimage retained on the photoconductive surface of a photoelectrostaticrecording member, said member having a base supporting said surface,said base varying in conductivity in accordance with changes in thehumidity of the surrounding atmosphere or the like, the combinationcomprising: developer means for applying electroscopic powder of apredetermined polarity to the surface of said recording member wherebythe latent image is converted into a visible form; a source ofelectrical power; electrode means coupled to said power source anddisposed adjacent said base support, said electrode mEans providing abias voltage having a polarity the same as that of said electroscopicpowder applied to said member for repelling the powder from the nonimageareas of the photoconductive surface of said recording member; andsensor means coupled to said electrode means and the base support ofsaid recording member for automatically regulating the operation of saidelectrode means to maintain said bias voltage at said predeterminedlevel in accordance with the conductivity of said base support.
 10. Thecombination as claimed in claim 9, wherein said sensor means includes apair of spaced conductors coupled to said base support and connected tosaid electrode means, said base support completing a circuit betweensaid conductors, whereby a change in conducting of said base supportcauses a corresponding change in current flow from said power sourcethrough said electrode means, thereby to maintain the level of said biasvoltage on said member for repelling said electroscopic powder.
 11. Inan apparatus for developing a latent electrostatic image retained on thephotoconductive surface of a photoelectrostatic recording member, saidmember having a moisture-sensitive base supporting said surface, thecombination comprising: developer means for applying electroscopicpowder to the surface whereby the latent image is converted into avisible form; a source of electrical power; a corona-type electrodedisposed adjacent said base support providing an electrical current tosaid member to produce a bias voltage of a predetermined level forrepelling the powder from the nonimage areas of said photoconductivesurface and including a discharge wire surrounded partially by aconductive shield, said wire being electrically connected to said powersource; a roller member mounted for rolling engagement with saidrecording member along the base support thereof, said roller memberincluding first and second electrically conductive halves insulativelyspaced from each other, said first roller half being connected to theconductive shield of said corona electrode and said second roller halfbeing connected to ground potential; and said first and second rollerhalves being electrically interconnected through said base support,whereby when the moisture content of said base support increases, theconductivity thereof increases proportionally, thereby to in turnmaintain said predetermined bias voltage for the repulsion of developerpowder from the nonimage areas of said photoconductive surface.
 12. Thecombination as defined in claim 11, wherein each of said roller halvesof said roller member comprises a conductive core extending axiallythereof with a cylindrical insulating jacket formed thereabout, andwherein said roller halves include mounted at opposing ends thereof,electrically conductive disc members, each of which is connected to arespective one of said conductive cores of said roller halves, said discmembers being joined by means of an insulating spacer and being inrolling engagement with the base support of said recording member.